1. Field of the Invention
The present invention relates to a compound having an asymmetric carbon atom, an oxidation-reduction reaction causing portion, and a liquid crystal substituent.
2. Description of the Related Art
Cholesteric liquid crystals are known to exhibit structural coloration similarly as in an opal structure or a thin film interference structure. The cholesteric liquid crystals have been utilized, in the past, in thermometers utilizing temperature dependency of the structural coloration or, recently, in display materials utilizing characteristics of having memory properties in a planer phase or a focal conic phase in a liquid crystal element or lasers utilizing a refractive index periodic structure, for example.
The cholesteric liquid crystals also include nematic liquid crystals (chiral nematic phase) having a twist structure utilized in common LCDs in a broad sense. Display materials using the cholesteric liquid crystals are used for displaying document information, displaying imaging information, and light modulation for electrically controlling light.
Thus, much research on display and light modulating materials utilizing a cholesteric liquid crystal phase have been conducted heretofore. As the cholesteric liquid crystal phase, a chiral nematic phase in which a chiral reagent has been added to a nematic liquid crystal has been utilized.
An extremely large amount of research on chiral reagents has been conducted for LCD application. In general, a chiral reagent has an asymmetric carbon atom in a molecule so as to spirally arrange liquid crystal molecules and is designed by introducing a liquid crystal portion into the molecule so as to increase the compatibility of the chiral reagent with the liquid crystal (International Publication No. WO 02/06195, pamphlet).
The selective reflection length of the cholesteric liquid crystal is indicated by multiplying the pitch length and the average refractive index as illustrated in the following Equation.λ=P·n  Equation
In the Equation above, P represents the pitch length, and n represents the average refractive index of the liquid crystal.
In toning of the structural color by the cholesteric liquid crystal, changes in the pitch length in the liquid crystal orientation direction are utilized, unlike in the case of the opal structure or the thin film interference structure. Therefore, there is an advantage in that volume changes do not accompany this utilization. Attempts to change the pitch length by external stimulus have been studied, and methods for changing the pitch length by heat or light have been proposed in Chemistry Letters, 199, 87-88 (1999) and Liquid Crystals, 27, 929-933 (2000).